(of a dog) is from 1810. Heeler "unscrupulous political lackey" is U.S. slang, 1877, from the notion of one who follows at the heels of a political boss, no doubt coined with the image of a dog in mind. Achilles' heel "only vulnerable spot" is from 1810. Heel-tap was originally (1688) one of the bits of leather that are stacked up to make a shoe heel; meaning "bit of liquor left in a glass or bottle" first recorded 1688; the exact connection is uncertain. Down at heels (1732) refers to heels of boots or shoes worn down and the owner too poor to replace them.